Your main point was about salary negotiation (and I don't know much about that) but your example about interviewing is interesting to me:

> I spent a full day interview [...] and yet I thanked every single interviewer for their time, and told them how much I appreciate [...]

Where I work we became very sceptic about this trait in candidates, especially if someone is overdoing it. Then the suspicion rises whether they are overcomensating for another trait they believe about themselves.

I feel that being likable is table stakes and not something you would optimize for that much.